Roofing granules with high solar reflectance, roofing products with high solar reflectance, and processes for producing same
Solar reflective roofing granules include a binder and inert mineral particles, with solar reflective particles dispersed in the binder. An agglomeration process preferentially disposes the solar reflective particles at a desired depth within or beneath the surface of the granules.
1. A process for preparing solar reflective roofing granules, the process comprising:
(a) providing an inorganic binder and inert mineral particles to form a mixture;
(b) forming the mixture into uncured granule bodies having an exterior surface;
(c) adhering solar reflective particles only at or proximate to the exterior surface of the uncured granule bodies; and
(d) firing the binder to provide the solar reflective roofing granules having the solar reflective particles only at or proximate to the exterior surfaces thereof.
2. A process according to claim 1 wherein the solar reflective particles are mechanically adhered to the exterior surface of the uncured granule bodies.
3. A process according to claim 1 , further comprising mixing the solar reflective particles with a fluid carrier to form a paste and adhering the solar reflective particles to the exterior surface of the granule bodies by applying the paste to the exterior surface of the granule bodies.
4. A process according to claim 1 further comprising sizing the uncured granules by screening.
5. A process according to claim 1 further comprising surface treating the cured roofing granules.
6. A process according to claim 1 wherein the inert mineral particles comprise uncalcined kaolin, the binder comprises metal silicate, and the binder is cured by heating the uncured granules at from about 500 degrees C. to 800 degrees C.
7. A process for preparing solar reflective roofing granules, the process comprising:
(a) providing an inorganic binder, ceramic particles and solar reflective particles;
(b) dispersing the ceramic particles and the solar reflective particles in the inorganic binder to form a mixture;
(c) forming the mixture into uncured granules, each uncured granule having a plurality of solar reflective particles homogeneously dispersed with a plurality of ceramic particles; and
(d) firing the uncured granules to form cured roofing granules, each cured roofing granule including a plurality of the solar reflective particles at or proximate to an exterior surface thereof.
8. The process according to claim 7 wherein the ceramic particles have an average particle size of from about 0.1 micrometers to about 40 micrometers.
9. A process according to claim 7 further comprising selecting the solar reflective particles to provide at least 60 percent solar reflectance to the cured roofing granules.
10. A process according to claim 7 further comprising sizing the uncured granules by screening.
11. A process for preparing solar reflective roofing granules, the process comprising:
(a) providing an inorganic binder and ceramic particles;
(b) forming the ceramic particles and inorganic binder into uncured granule bodies having an exterior surface;
(c) adhering solar reflective particles only at or proximate to the exterior surface of the uncured granule bodies; and
(d) sintering the uncured granule bodies to form solar reflective roofing granules having the solar reflective particles only at or proximate to the exterior surfaces thereof.
12. A process according to claim 11 wherein the solar reflective particles are mechanically adhered to the exterior surface of the uncured granule bodies.
13. A process according to claim 11 further comprising providing a sintering binder and mixing the sintering binder with the ceramic particles to form a mixture and subsequently forming the mixture including the ceramic particles into uncured granule bodies.